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Plants and climate • Q: Does the forest make the rain or the rain make the forest? • In Roman times, Egypt and the north of Africa was green and wooded – goats and deforestation changed the climate • Forests cool the air, increase the humidity, increase chance of rain • How much damage are humans doing by cutting down large tracts of the Amazon Forest !! Warm and cold fronts • Air masses named for their origin (polar, tropical, equatorial) and moisture content (maritime, continental) • Sharp boundaries occur between warm & cold air masses – called fronts • Warm air always move up higher than cold air • Warm front – advancing warm air replaces receding cold air, gentle slope to transition, steady rain • Cold front – advancing cold air pushes up receding warm air, steep slope to transition, heavy rain & storms • Australia weather mostly experiences cold fronts Precipitation and Clouds • Adiabatic cooling occurs when moist air rises • Air becomes saturated, allowing condensation and precipitation as rain, hail or snow • Different types of cloud associated with rain, some contain ice • High clouds (> 5 km) – eg cirrus, ice crystals • Middle clouds (2-7 km) – eg altostratus, mostly water • Low clouds (< 2 km) – eg stratus (rain), nimbostratus (snow) • Vertically developed clouds (via convection) – eg cumulus, cumulonimbus (thunderstorms) Thunderstorms • Friction causes build up of charge • If strong electric field, ionises air which provides a conducting path for currents – lightning strikes (flash & thunder) • In thunderstorms – don’t stand under (isolated) trees, hold golf clubs! • Do stay in a car, if outside crouch down with feet together. • Note: If your hair starts to stand on end, run! • Storms - unstable layers of cold over warm air, strong convection 1 Cyclones, hurricanes, typhoons • Extreme weather systems – low pressure cells, clockwise rotation in southern hemisphere (Coriolis force) • Name for storms is regional: cyclone is general term (also used in Australia, Indian Ocean), hurricane (N Atlantic, NE Pacific) & typhoon (NW Pacific) • Only found in latitudes 8° - 20°; driven by pressure differences & Coriolis force Cyclones (2) • Cyclones – start over warm oceans, unstable moist air and strong convection currents, often triggered by thunderstorms, diameters 200 – 800 km, winds up to 300 km/h, system moves slowly • Tornadoes – diameters < 100 km, winds > 500 km/h, fast moving, occur as waterspouts over oceans • Cyclones named for ease of communication – started by an Australian in early 20th century; originally female names, now both male & female, birds, flowers etc Main ideas to take away • Atmosphere – necessary for life to exist in comfort • Water cycle – principal factor influencing the weather patterns • Sun – main energy source, from electromagnetic radiation • Thermodynamics – underlying physics; relationships between heat flows and internal energy (can be measured by temperature) 2